Whilst most of semiconductor thin films are prepared from inorganic materials containing metals, progress has also been made in developing organic semiconductor thin films. Currently, conventional approaches for making organic semiconductor films include spin-coating, drop casting, doctor blading and vacuum thermal evaporation. However, there are several drawbacks associated with the above processes, for example, formation of pinholes in the film, poor uniformity, low production rates or low conductivity.
To date, graphitic carbon nitride (g-CN), the most stable allotrope of carbon nitride, has emerged as a promising material for manufacturing optoelectronic devices owing to its electronic structure and photoelectronic properties. It may be applied as a photocatalyst for fuel conversion, degradation of organic pollutants, bio-imaging, and sensing. However, most of the current methods for preparing g-CN films are still at the preliminary stage and far from satisfactory. In particular, the g-CN films are mainly prepared from g-CN powders which are usually obtained from thermal condensation of organics (e.g. urea, melamine, and thiourea) under vacuum condition. The powders obtained are subsequently subjected to direct depositions including drop casting and spin coating. However, these approaches fail to fabricate g-CN films with good uniformity, conductivity and stability.
Most recently, a thermal condensation method of depositing the g-CN nanostructures by placing precursors between two substrates or on a substrate has been reported (M. Shalom, S. Gimenez, F. Schipper, I. Herraiz-Cardona, J. Bisquert, M. Antonietti, Angew. Chem. Int. Ed. 2014, 53, 3654-3658; Angew. Chem. 2014, 126, 3728-3732; J. Xu, T. J. K. Brenner, L. Chabanne, D. Neher, M. Antonietti, M. Shalom, J. Am. Chem. Soc. 2014, 136, 13486-13489). However, the high process temperature strengthens the adhesion force of the powder on the surface, making it difficult to be cleaned out and resulting in non-uniform films (as shown in FIG. 1).
Accordingly, there remains a strong need for developing an effective method to prepare a semiconductor film, especially for metal-free semiconductor thin film, with good uniformity and conductivity. The method should also allow for adjustment of the surface morphology, thickness and size of the film.